1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device to which magnetic domain wall movement is applied.
2. Description of the Related Art
Data storing devices are divided, for the most part, into volatile data storing devices that lose all recorded data when power is turned off and non-volatile data storing devices that keep data even when power is turned off.
Non-volatile data storing devices include a hard disc drive (HDD) and a non-volatile random access memory (RAM). The HDD includes a read and write head and a rotating data recording medium, and can store data of 100 gigabites or more. However, a device that has a rotating part like the HDD wears down over time, and thus, there is a high possibility of failure, thereby reducing reliability.
A flash memory which is widely used is an example of non-volatile RAM. However, the flash memory has the drawbacks of having slow reading and writing speeds and having a short life span. Due to the drawbacks of the flash memory, new memory devices such as ferroelectric random access memory (FRAM), magnetic random access memory (MRAM), and phase change random access memory (PRAM) have been developed in limited numbers and a few have been commercialized. However, it is difficult to develop the FRAM in the form of a large capacity memory due to the difficulty in reducing a cell area, and it is also difficult to develop the MRAM in the form of a large capacity memory since the MRAM has a large writing current and has a small sensing margin for distinguishing data signals. The PRAM is relatively easier to reduce to a minute size compared to the FRAM and MRAM, but a reduction of reset current is needed to reduce power consumption. Also, the flash memory, FRAM, MRAM, and PRAM all have small storage capacities when compared to a HDD and have high manufacturing costs.
Therefore, as a method of solving the drawbacks of the conventional non-volatile data storing devices as described above, much research and development with respect to a new data storing device that uses a magnetic domain wall movement has been carried out.
A magnetic domain in a magnetic substance and magnetic domain walls will now be described. Afterwards, a storing device that uses the magnetic domain and the magnetic domain walls will be described.
A minute magnetic region that constitutes a ferromagnetic body is named a magnetic domain. The rotation of electrons in a magnetic domain or the direction of magnetic moment is identical. The size and magnetization direction of a magnetic domain can be appropriately controlled by the shape and size of a magnetic substance and external energy.
A magnetic domain wall is a boundary portion of a magnetic domain having a magnetization direction different from another magnetic domain. The magnetic domain wall can be moved by an external magnetic field or by a current applied to a magnetic substance. A plurality of magnetic domains having a specific magnetization direction can be formed in a magnetic wire having a predetermined width and thickness, and the magnetic domains can be moved using a magnetic field or an electrical current having an appropriate intensity.
The principle of the magnetic domain wall movement can be applied to data storing devices such as HDD's. That is, an operation of reading/writing data is possible when the magnetic domains magnetized so as to correspond to specific data in a magnetic substance are moved in order to pass through a read/write head. In this case, a reading/writing operation is possible without directly rotating a recording medium. Accordingly, the problems of wearing down and failure of a conventional HDD can be solved. An example of a data storing device to which the principle of magnetic domain wall movement is applied has been disclosed in U.S. Pat. No. 6,834,005 B1.
Also, the principle of magnetic domain wall movement can be applied to a memory such as a non-volatile RAM. A non-volatile memory device that can write/read data of ‘0’ or ‘1’ whereby a voltage in a magnetic substance varies according to the movement of magnetic domain walls in the magnetic substance having magnetic domains magnetized in a specific direction and magnetic domain walls. In this way, since data can be read and written by varying the positions of the magnetic domain walls by flowing a specific electrical current in a line type magnetic substance, a highly integrated device having a simple structure can be realized. Therefore, when the magnetic domain wall movement is used, the manufacture of a memory having a very large storage capacity compared to the conventional FRAM, MRAM, and PRAM is possible. An example of applying the principle of magnetic domain wall movement to a memory like RAM has been disclosed in Korean Patent Publication No. 10-2006-0013476.
However, the development of semiconductor devices that use the magnetic domain wall movement is still in its initial stages, and there are a few problems that have yet to be solved in order for them to be used in practice.
In order to ensure the stability of movement of the magnetic domain walls, an artificial notch is generally used. FIG. 1 is a perspective view illustrating a conventional U shaped magnetic wire 100, which has been disclosed in U.S. Pat. No. 6,834,005 B1. Reference numerals 10 and 15 in FIG. 1 respectively indicate a magnetic domain corresponding to 1 bit and a magnetic domain wall. FIG. 2 is a plan view illustrating a conventional magnetic wire 200 having notches, which has been disclosed in Korean Patent Publication No. 10-2006-0013476. Reference numerals 20 and 25 respectively indicate a magnetic domain and a magnetic domain wall. As depicted in FIGS. 1 and 2, the notches are grooves formed on both sides of the magnetic wires 100 and 200 corresponding to portions where the magnetic domain walls will be formed, and function to stably stop the moving magnetic domain walls.
However, the formation of notches having a minute size on a magnetic wire having a thickness and width of a few tens of nanometers is practically very difficult. Furthermore, the formation of minute notches having a uniform gap, size, and shape is even more difficult. If the gap, size, and shape of the notches are not uniform, the characteristics of a device are non-uniform since the intensity of a pinning magnetic field that stops the magnetic domain wall movement varies according to the gap, size, and shape of the notches.
Therefore, the use of notches to stabilize the movement of the magnetic domain walls is inappropriate in view of process readiness and the uniformity of device characteristics. Therefore, there is a need to develop a technique that can stably move magnetic domain walls in 1 bit units without using the notches.